I like trying to get a DC, (Direct Current), type signal into
computers using home brew gear to do it...
On current(ish) hardware and modern OSs this is pi$$ easy
as there are kits or pre-built interfaces to help...
I do it big time for the AMIGA to use the AMIGA as an
integrated electronic test set, multitasking differing parts
of that old tub as say a Function Generator, Test Card
Generator, 8 channel Logic Analyser, Oscilloscope and many
more.

Only one thing has stumped me and NO-ONE I have asked
on different MLs and Forums has ever come up with an answer.

However I have now come to my second major hurdle and
suspect I can`t do it...

Here goes...

Well as some of you are aware I`m getting into MikeOS
at the moment and it is easily capable of getting a DC signal
into the computer using the Parallel Port and Serial Port.

Here is the MAJOR drawback however...

How do I do exactly the same on say a notebook like this
HP dual core notebook of mine that hasn`t got a Parallel
and Serial Port using MikeOS???

Yup, the OS is derived entirely from BIOS routines hence the
unavailability of such luxuries...

Even the sound "card(s)" don`t exist during POST and cannot
be accessed through MikeOS as the hardware does not have
8 bit backwards compatibility these days. If it was available
at ancient hardware level then V-F conversion would be dead
easy...

> Does the laptop have a PS2 port?

Nope, and if memory serves me correctly neither do current
netbooks. Although they CAN boot from USB, that is a function
of INT 19 IIRC...

> In that case, it is probably a soldering iron job to install a
> keyboard wedge.

Hmmm, not really practical...

I`d seriously thought of the possibility of disabling interrupts
and banging the VGA ID lines to allow TTL level V-F conversion
to take place under SW control. I don`t know if ALL current
netbooks, notebooks and laptops have VGA facilities.

Wild idea. Maybe one of the I/O ports has a power supply line that is monitored by the system, and is accessible at BIOS level: hook up a couple of resistors in series with it, and connect your DC level to the junction. Ideally you'd be able to monitor the supply current, but maybe a suitable choice of resistors (and maybe a hefty DC amp) would provide adequate voltage change.

"Klinger, do you know how many zoots were killed to make that one suit?" — BJ Hunnicutt, 4077 M*A*S*H

Wilder than you think. Some serious research shows that
access to IDs 0 - 2, (3?), is restricted or not possible due to
the conflicting nature of how it works. I have done some
basic disassembling of the video bios and boot bios but not
found the area yet that detects at least ID0 at 0, zero, TTL
level... :-(

As for the USB idea, I daren`t even think about "VCC loading"
as my projects are aimed at 10 year olds to build for themselves.
Anything that is likely to cause serious damage to the computer
is a No No...

And ollie...

This is for MikeOS and if you haven`t tried it yet it has some
serious limitations. This is why I`m getting into it with some
of my projects ported to it and thoroughly enjoying it.

1) The whole OS runs in one 16 bit SEGMENT ONLY.
(Not strictly true but close enough... :)
2) All of the OS relies entirely on legacy BIOS routines.
3) There is ONLY 32KB of memory to code in and that can be
MIKE-BASIC and/or assembly code.
4) The BASIC interpreter, IS BASIC, by any other name.
5) ONLY COM1/ttyS0 is available at boot in two baud rates.
(The parallel port is available in SPP mode only.)
6) USB boot IS possible as this is a function of INT 19; this
is an extension that is transparent to the user. I use a USB
floppy on this notebook for MikeOS.
7) AFAIK legacy USB is for USB 1.0 only, but I could be wrong
nowadays as it was some years ago when I reasearched it.
This means KB, (and Mouse???) ONLY; so therefore no serial
ports... Nice try though... :)
8) All I/O, (note:- NOT video DMA), is inside the standard base
memory 0 - 2, (-4?) KB as is normal. From this fact I am
wondering if I/O address 220h is available for legacy sound
access. It is never shown on serious current OSs as it is not
required but I may be able to enable a sound card at
assembly level to use the "recorder", (Mic), input and use it
as a VCO input. The problem with this is ancient sound cards
used IRQ 5 or 7 to enable and we have progressed to IRQ 23
for this notebook and I`m not sure at this point in time
whether high IRQs are recognised in REAL mode.